The use of a sensor network including sensor nodes capable of various operations and communications are extending to various application fields such as forest fire monitoring, intrusion monitoring, real-time target tracking, emergency relief systems, and real-time traffic information collection.
Examples of the existing sensor networks are centralized sensor networks and unmanned real-time sensor networks.
In a centralized sensor network, sensing information acquired by each sensor node is transmitted through a sink node to a server, and the server collects the sensing information transmitted.
A self-control sensor network is an unmanned real-time sensor network in which each node or a node group senses a certain event and transmits a control command to an actuator to operate the actuator in order to intelligently determine a certain situation.
Evolving from the existing sensor system of performing a simple sensing operation by a sensor node through a sensor and transmitting the sensing data, a sensor network system such as self-control sensor network processes sensing data, forms a group of nodes in order to determine a certain situation, and requires cooperative communication based on the formed group. Thus, in a self-control sensor network, sensor nodes need be more intelligent and energy-efficient. Also, if necessary during operation, the sensor nodes remotely download an execution code to perform a new program.
A set of nodes sharing one independent program code is called a group. Herein, an independent program needs to communicate with another program. This means the inter-group communication of nodes that executes their respective programs. What is therefore required is a method for creating/constructing a group dynamically, discovering member nodes of a target group in the network under the condition of occurrence of inter-group communication, searching/establishing a communication path, and exchanging messages.
The existing group discovery/communication methods may be classified into two approach methods.
In the first method, a member node broadcasts a group service advertisement through a network to notify group information related to a certain service. When receiving the advertisement, a node stores the related group information in a local cache memory. Accordingly, the local cache is first searched for later group communication.
In the second method, on-demand group discovery is performed through a group service request. In this method, a node desiring communication generates a group discovery request message for a target group, and a member node of the target group receives the request message and generates a reply message to discover a group member.
However, the above approach methods increase the network resource consumption because they broadcast a group service advertisement or a group service request to every node. A unicast-based discovery method is to overcome the above limitation of the broadcast-based discovery method. However, the unicast discovery method may fail to discover a group member node.
In order to complement the broadcast-based group service discovery method, a method is used that broadcasts a group service advertisement or a group service request message by a predetermined hop count. However, if the hop count is incorrectly set, this method may generate excessive messages or may fail to discover a group member node.